what fuse is what and are any of the missing ones important?

SonOfaTomP

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been trying to figure out why both my heat and defroster don't work. horn is also broke but that much just be the horns themselves as those have broke on all m bodys we've had. checked the fuses and saw that several were missing. put new ones in and they just fell out. i can't seem to find my repair manual so i'm asking yall what does each of these fuses do and will they fix my issues? i know that the HVAC system has a vaccum problem on many of these cars so i might have to check that. car is an 88 fury

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Camtron

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Does your blower motor turn on and your not getting heat out of it or nothing is turning on period?
That green 30amp fuse, bottom left of the picture, is your heat/AC fuse.
 
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Aspen500

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Looks to me the missing fuses are not used on your car. If you look, there's either only one terminal, or no terminals in the slots for the fuse prongs. Looks like the spot that has 2 terminals is for power locks/power seat.

Like Camtron asked, do you mean the blower motor doesn't work or you can't switch modes between vent, heat and defrost? Also, do you have heat only or manual heat andA/C, or automatic climate control?
 

Darth-Car

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Yeh Aspen500 kind of beat me to it, but these cars came from the factory with fuse panels that were designed to accommodate all option packages. If your car did not have a specific option, then you just did not get that fuse. I only worry if I see a bunch of fuses missing, or a fuse that should be there, like a horn fuse, and it is missing.
 

Camtron

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Yea, does your car have electric door locks/seats and power windows? Looks like there's spade terminals in both locations but not fuses...if you don’t have them, looks like you have available 12v power for future accessories.
 

SonOfaTomP

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car is a roller up window car. looked in a AHB car to see that it had extra fuses so i was confused. i'm guessing police cars are different. took the dash off to see this. HVAC hoses are broken like on so many of these cars. looked at two videos and a diagram but i'm still a little confused on what goes where.

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BudW

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This is the fuse box pin-out for ’88 M’s (which most likely will not be the same pinout as other year M’s). As mentioned, not all slots were used according to how vehicle was equipped. If you have empty slots, sometimes they have power going to it (full time or when key is on), but the other end connector will be missing. A little work and easy power tap w/fuse for add-on accessories.
88 Fuse Box.jpg

Note: there is a horn relay that sometimes goes bad, on the fuse box.
BudW
 

BudW

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This portion of the 7-way vacuum connector tends to crumble after 15-20 years.
My recommendation is to cut off both sides of that connector (not at once, though) at the mid connector and splice with regular vacuum hose. I can’t remember what size the hose is, but you can always take a “cut-off” piece of the plastic hose to auto parts store.
A splice that is a bit longer than 1” (3 cm) works great. No need for glue or tape (unless you wanted to).

What I do after the splice job is complete, is take some colored Sharpies and add some color on the “black” hoses in case you need to take something apart again down the road. Most plastic tubing is colored, but some are all black.

There are three different 7-way vacuum connectors on your car. One at the A/C control head and the other two at a junction in the vicinity behind the ashtray. All three of those 7-way connectors can crumble on you just by looking at it wrong. The hoses are generally good, just the cheap material used for the connectors.

Annotation 2019-12-17 171300.jpg

This is out of my ’86 FSM (Factory Service Manual) for heater only (not sure if your car is A/C or not). A/C hose diagram is in a PDF file at bottom of this post.

Annotation 2019-12-17 172134.jpg

This is for A/C with SATC (Semi Auto Temp Control) – but I ran arrows to vacuum hoses to help you identify them
Purple arrow is the mid-way 7-way connector.
Gray arrow is black and gray hose that goes through firewall at spot shown) to manifold (vacuum source) and hot water valve.
Red arrow goes to defrost door vacuum motor
Purple arrow goes to A/C mode door motors (upper and lower)
Green arrow goes to recirculation door motor.

Annotation 2019-12-17 175138.jpg

The A/C vacuum hose pinout is
1 Dark Green (Recirculation door) and Gray (hot water valve)
2 Red (mode door)
3 Black (vacuum source – intake manifold)
4 (sealed off)
5 Brown (mode door)
6 Yellow (defroster door)
7 Light Green (recirculation door)

The black hose under-hood can get brittle and break is not treated well - but it can also be patched up using a short piece of vacuum hose. If the black hose is broken, then there will not be any vacuum to operate the vacuum motors.

I hope this helps.
BudW
 

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  • 86 FSM pg 24-47a.pdf
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SonOfaTomP

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i've made another thread on my on going repairs to the hvac system. i have connected all 7 of the hoses using wiper hosing, all except one. i havent a clue as to where the grey one goes. anyway about fuses. is there one that goes to the speakers? i ended up messing up my radio after taking it out to work on the hoses and now my speakers don't work. should be OEM speakers. took out the radio and put in a jeep oem radio and also got no sound from the speakers. either they're both broke or i'm just stupid.
 

Camtron

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I think you need a test light or multi meter, my friend....you need to be able to check for voltage at speaker connections, blower motor for the Ac/heater, fuses ect...
There’s a fuse for the radio (5amp fuse in your photo), radio head sends power to speakers when the radio head is turned on. If the radio head itself is turning on, then theoretically, voltage should be going to your speakers as well; unless there’s a short somewhere.
I couldn’t tell you what or where the grey hose goes to, I’ve not had to mess with my heater/Ac yet.
 

SonOfaTomP

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I think you need a test light or multi meter, my friend....you need to be able to check for voltage at speaker connections, blower motor for the Ac/heater, fuses ect...
There’s a fuse for the radio (5amp fuse in your photo), radio head sends power to speakers when the radio head is turned on. If the radio head itself is turning on, then theoretically, voltage should be going to your speakers as well; unless there’s a short somewhere.
I couldn’t tell you what or where the grey hose goes to, I’ve not had to mess with my heater/Ac yet.
pulled the head off the old one to get a tape out, bent its prongs that connect the face plate to the radio. tried to straighten them with a knife (i know very smart) that caused a spark, but whats interesting is that while messing with the prongs the radio turned on and tuned with no face plate. hope i didn't fry the oem wires. changed my radio fuse but i'll check the other ones just in case. FA manual i have says radio needs a 10 but my car always had a 5 in that spot so i replaced it with a 5. not sure if they're different.
 

SonOfaTomP

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This is the fuse box pin-out for ’88 M’s (which most likely will not be the same pinout as other year M’s). As mentioned, not all slots were used according to how vehicle was equipped. If you have empty slots, sometimes they have power going to it (full time or when key is on), but the other end connector will be missing. A little work and easy power tap w/fuse for add-on accessories.
View attachment 38528
Note: there is a horn relay that sometimes goes bad, on the fuse box.
BudW
thats very useful. manual doesn't list that stuff. thanks.
 

Camtron

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I have a spare, Power Pro 3 in my old tool box; I’ll send it to you as a Christmas present.
It was a game changer for me when I first got it. Connect it to your battery and you can use it to check voltage and grounds and even use it to power up electrical circuits (you can easily fry things if you don’t know what you’re doing)
I still use one from time to time but, I normally use a, Load Pro with my Fluke meter these days.
 

SonOfaTomP

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I have a spare, Power Pro 3 in my old tool box; I’ll send it to you as a Christmas present.
It was a game changer for me when I first got it. Connect it to your battery and you can use it to check voltage and grounds and even use it to power up electrical circuits (you can easily fry things if you don’t know what you’re doing)
I still use one from time to time but, I normally use a, Load Pro with my Fluke meter these days.

oh don't worry about that now. my dumbass didn't plug the thing all the way in! but tell you what if you still got that cars OEM radio i'd be interested in that, especially if its got the chrome face plate. the jeep radio i have in my car now doesn't really fit the aesthetics of the car and it's cassette deck doesn't work. i appreciate that a lot though
 

Camtron

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oh don't worry about that now. my dumbass didn't plug the thing all the way in! but tell you what if you still got that cars OEM radio i'd be interested in that, especially if its got the chrome face plate. the jeep radio i have in my car now doesn't really fit the aesthetics of the car and it's cassette deck doesn't work. i appreciate that a lot though
I do have it, but, it doesn’t work at all (even has a tape stuck in the deck). I need to find an old stereo/speaker repair shop; unfortunately there’s not many of them left around here.
 

SonOfaTomP

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I do have it, but, it doesn’t work at all (even has a tape stuck in the deck). I need to find an old stereo/speaker repair shop; unfortunately there’s not many of them left around here.
damn son. oh well, guess i gotta keep looking. thanks tho
 
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